In a mobile base station communications system, currently, there are two commonly used manners of adjusting a downtilt angle of an antenna, that is, manual adjustment and electrical adjustment. Compared with the manual adjustment, the electrical adjustment does not require a worker to manually climb a tower or perform operations at an antenna end, presents great convenience, and is easy to implement. At present, especially in a developed area and in a relatively developed area, electrical adjustment gradually becomes a mainstream and is applied more and more widely.
The limitation of mobile base station site resources has resulted in an increasing demand for a multi-band antenna. For the multi-band antenna, currently, a mainstream electrical adjustment manner is that an antenna at each frequency band uses one downtilt angle adjustment apparatus, that is, one multi-band antenna needs multiple downtilt angle adjustment apparatuses. However, because such a downtilt angle adjustment manner of the multi-band antenna needs multiple downtilt angle adjustment apparatuses, an overall size of an antenna downtilt angle adjustment apparatus is large, thereby failing to meet a development trend of miniaturization.